The present invention is in the field of continuous casting of molten metal and relates to continually synchronizing the travelling movement of two revolving edge dam chains during casting in a twin belt, continuous casting machine. More particularly the invention relates to continual synchronization of travelling movement of two revolving edge dam chains having lug-molding pockets for casting aligned projecting lugs on opposite edges of a continuously cast metal slab, shown as a stream of copper anodes having opposite pairs of aligned lugs maintained in suitable alignment on their side edges.
A conventional way to mount copper anodes in an electrolytic refining tankhouse is to provide lugs projecting from opposite edges of the anodes at their upper ends for vertically hanging each anode by its lugs. It is important to have these lugs positioned in suitable alignment opposite each other. Thus, all anodes hanging in a row in a tank supported their respective lugs are vertically positioned and their edges are equally spaced from opposite sidewalls of the tank for providing a straight level row of accurately positioned, separated and aligned anodes.
It is a fairly recent development, but now conventional, to continuously cast an endless slab of anodes having their upper ends connected to lower ends of adjacent anodes. Then, downstream from the casting machine the endless slab is sheared at spaced intervals for separating individual anodes. Each anode has a pair of projecting lugs integrally cast onto its opposite edges. For the two lugs on each anode to be cast in suitable alignment with each other, it is necessary that the two revolving edge dam chains in a twin-belt, continuous casting machine have their lug-molding pockets continually synchronized in their movement along opposite edges of the casting region in the machine.
As background information, a reader of the present specification is referred to U.S. Pat. No. 4,150,711 dated Apr. 24, 1979, titled xe2x80x9cMethod and Apparatus for Continuously Casting Metal Slab, Strip or Bar with Partial Thickness Integral Lugs Projecting Therefromxe2x80x9d and U.S. Pat. No. 4,586,559 dated May 6, 1986, titled: xe2x80x9cProcess and Apparatus for Casting a Strip with Laterally Extending Lugsxe2x80x9d. These Patents show two revolving edge dam chains (also called xe2x80x9cside damsxe2x80x9d) having lug-molding pockets therein in a belt-type casting machine for continuously casting an endless slab of anodes having lugs projecting from their opposite edges. These revolving edge dam chains are shown being synchronized in their travelling motion along opposite sides of the moving mold region. They are driven by friction forces of contact with the caster belts, and therefore travel at approximately the same speed as the caster belts.
A conventional way to construct such edge dam chains is to assemble a multiplicity of metal dam blocks, typically manufactured from nonmagnetic copper alloy, strung onto a flexible metal strap, for example a stainless steel strap. After the dam blocks have been strung onto the strap, the ends of the strap are joined as known in the art to form an endless loop. Such an edge dam loop also is called a xe2x80x9cdam block chainxe2x80x9d. Being formed of metal, edge dams have a positive temperature-coefficient of thermal expansion. Thus, increasing temperature of one edge dam chain in a continuous casting machine relative to temperature of the other will slightly increase the overall length of the hotter one relative to the overall length of the less-heated one. The higher-temperature (longer) edge dam chain will require slightly more time to complete one full revolution compared with the lower-temperature (shorter) edge dam chain; for example, the longer will lag slightly behind the shorter.
The above-referenced U.S. Patents have been assigned to the same Assignee as the present patent application. Pat. No. 4,586,559 discloses controlling the relative temperatures of two revolving edge dam chains by using liquid-spray coolers and high intensity burner heaters.
A high intensity burner is a noisy, natural gas burner. Its flames are applied directly to the blocks of a revolving edge dam. Such burners exhibit many severe disadvantages.
They are extremely noisy, being stressful and detrimental to caster operating personnel, even though such personnel are wearing ear protection. Only about 20% of heat released by the intense flames of a high intensity burner goes into the dam blocks themselves. Approximately 80% of excess heat flows into spaces underneath and near the casting machine. When continuously casting an endless slab of copper anodes as shown, such casting often is carried out at a production rate reaching 100 tons per hour of xe2x80x9canode copperxe2x80x9d, also called xe2x80x9csemi-pure copperxe2x80x9d. During such a casting operation, at least about one-half million (500,000) British thermal units (Btus) per hour of heat issue from the intensely-firing burners. Such heat emission occurs periodically depending on the need to change the temperature of either dam block chain relative to the other.
Thus, an enormous amount of excess heat, carried by intense flames of the burners aimed toward the edge dams, actually enters into places under and around the caster. This excess heat is very difficult to manage. It is detrimental to water seals, sensors, instrumentation, wiring, piping, crescent roller bearings, etc., and is detrimental to the environment of caster operating personnel. In summary, disadvantageously dissipating and attempting to manage at least about 500,000 Btus per hour of excess heat energy being periodically generated by intense, noisy burners is detrimental, troublesome, inefficient, and difficult to control.
In accord with the present invention, there are provided method, system and apparatus enabling successful, practical, controllable, electromagnetic induction heating of nonmagnetic copper alloy edge dam blocks in edge dam chains having lug-molding pocket blocks therein. For casting a continuous slab electrolytic anodes having lugs protruding from opposite edges of the cast slab, wherein lugs on these opposite edges must be cast in aligned opposed relationship, the lug-molding pocket blocks in the two revolving edge dam chains must be kept suitably aligned with each other as they travel along opposite sides of a moving-mold casting region in a twin-belt continuous casting machine.
A thermal-sprayed layer of ferromagnetic material is applied in a shallow depression formed in top surfaces of all regular dam blocks in an edge dam chain.
An induction heater assembly is operatively associated in induction heating relation with each edge dam chain. These induction heater assemblies, as shown, include a low-friction, thin skid plate of nonferrous material. This skid plate enables top surfaces of the dam blocks (i.e., their top surfaces which are coated with and are substantially all covered by a thermal-sprayed layer of ferromagnetic material applied to all regular blocks) to slide in closely spaced relationship past an induction heater coil configured for efficiently electromagnetically coupling with the layers of ferromagnetic material on blocks of a revolving edge dam chain.
A flux concentrator is positioned close to the induction heater coil for enhancing efficient coupling of the electromagnetic field with the ferromagnetic layers on the dam blocks of the revolving edge dam chain. These ferromagnetic layers become heated by induction heating. Their heat energy is readily conducted from their relatively large surfaces into the copper alloy dam blocks.
As shown, the thin ferromagnetic layer applied into a shallow rectangular depression on each dam block covers at least about 75% of the overall area of the top surface of the dam block.
A narrow shoulder of the dam-block material surrounds the shallow rectangular depression. The ferromagnetic coating has a thickness in a range of about 0.015xe2x80x3 (about 0.38 mm) to about 0.025xe2x80x3 (about 0.64 mm). This ferromagnetic material is thermal sprayed within this shallow depression in a thickness whereby the resulting overall block height xe2x80x9cHxe2x80x9d is the same as before the depression was formed in the top surface of the block.
The novel induction heating of copper alloy dam blocks in a revolving edge dam chain provided by the method, system and apparatus disclosed advantageously is quiet and is inherently efficient because the induction heating occurs in the ferromagnetic layer on a dam block. Thereby, heat energy being provided into this layer readily is conducted into the highly thermally-conductive copper alloy material of the dam block.
Moreover, the novel induction heating assembly advantageously is cool in relation to its overall environment and provides a very precise temperature control.